Many different propeller systems are used both for extracting energy from flowing fluid stream, or for example for driving a boat or airplane or the like through fluid.
Windmills may be classified into three basic classes; the horizontal axis lift type which is simply a propeller oriented with its axis of rotation substantially parallel to the wind direction and normally with its blades extending substantially perpendicular to the axis of rotation. These systems are conventionally used and are similar to propellers used to propel an airplane or as the screw for driving the ship or boat through the water.
It is also known to orient the axis of rotation of the windmill or the like substantially perpendicular to the direction of relative fluid flow. Such devices incorporating a drag type impeller are known as Savonious mills and those having a lift type impeller are known as Darrieus windmills.
Darrieus type windmills are shown in U.S. Pat. No. 1,835,018 issued Dec. 8, 1931 to Darrieus and U.S. Pat. No. 4,112,311 issued Sept. 5, 1978 to Theyse. U.S. Pat. No. 1,100,332 issued Jun. 16, 1914 to Smith appears to be a combination of the Savonious and Darrieus type windmills.
U.S. Pat. No. 4,390,148 issued Jun. 28, 1983 to Cudmore, discloses a rotary wind device wherein the axis of rotation of the rotor is oriented to be substantially parallel to the direction of intended movement but with a slight upward tilt to provide lift.
Some years ago Dr. Gunther Wagner built a prototype wind mill using two blade sections oriented at 90.degree. and mounted on a shaft the axis of which was at an angle of 45.degree. to the blade sections and oriented so that in one position one of the blade sections is horizontal while the other is vertical.